ScuzzBlog: Diaries May 2023

Entry 3rd May 2023: Post 1: Commodore 9R25 - Portable mini computer.

Commodore 9R25 - Portable mini computer.

The year is 1976 and I was working as a trainee architectural
technician at Walsall Architects. Part of my training involved
one day a week attending Wolverhampton Polytechnic where I was
studying for my HNC in Building Construction so that I could
become a member of MSAAT. It was during this time that my brother
left home and to join the RAF. Whether by choice or by simple
acquisition he gifted me his Commodore calculator. The very very
trusty Commodore 9R25. The calculator would partner me throughout
my final years of HNC and Advanced HNC, IOB and then during my
full time at School of Architecture.

Little did I know at the time that the calculator was actually
being marketed as a 'mini computer', making this my first official
Commodore computer. Twas a sad day when she packed up and I still
haven't been able to open the calculator to remove the batteries.

So on to today and my decision after some 47 years to finally
replace the calculator with a working version. This time complete
with box and electrical adaptor. I do love the buttons on this
machine. Reminds me of Gerry Anderson's UFO.

Just out of interest the calculator runs on a MOS MPS 7545 which
is a MOS Technology Inc Calculator Chip for an 8 (9)digit display.
She has 25 keys 9 blue, 5 red, 11 white. Generally an arithmetic
machine with a VFD display of 8(9) digits algebraic logic. Made in

'Your new calculator features a 4 key memory, square root, x squared,
reciprocal and percentage'.

'Your calculator thinks with People Logic. Engineers refer to it
as Algebraic Logic'. This simply means that your machine accepts
examples in the very same sequence as you would think out a problem'.

Basic Four Function Chain Operation

'Your calculator will chain through each of the four functions:
you can multiply after adding, divide after multiplying, subtract
after adding, and so forth, without re-entering the last figure
in the display'.

Technically the calculator has 9 digits in the display with the
left most used to indicate 'Overflow' say for example.

Sadly I was not able to play League of Legends on the calculator
but then the display is very small... That was a stack overflow
joke. Anyhoo I now have working versions of all my main computers
and calculators from 1976 right thro to 2023. How cool is that.

Commodore 9R25 - Portable mini computer.

My original calculator from 1976.

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Last updated 3rd May 2023

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